The present invention relates to a low-pressure casing for a brake booster for automotive vehicles comprising two sheet-metal casing shells which are sealingly interconnected at the casing periphery, an axially movable wall sealingly subdividing the low-pressure casing into a low-pressure chamber and a working chamber and fastening screws engaged at opposite end walls of the low-pressure casing to connect the low-pressure casing to a master brake cylinder and to the vehicle.
In low-pressure brake boosters for automotive vehicles, the master brake cylinder is fitted to the one end wall of the low-pressure casing, while the other end wall is fastened to the automotive vehicle, preferably to the splash-board. The brake forces which are transmitted onto the actuating piston of the master brake cylinder when braking will have to be re-transmitted as reaction forces from the master brake cylinder onto the point where the brake booster is fastened to the automotive vehicle. Taking into consideration that these comparatively high tractive forces take their course via the low-pressure casing, the low-pressure casing has so far been of a comparatively thick-walled construction, which acts adversely to a generally desired reduction of the brake booster's weight.
A substantial reduction in weight by use of a low-pressure casing construction with thin walls may be achieved by having the tractive forces transmitted via tie elements extending through the interior of the low-pressure casing, for instance, via tie bolts, as disclosed in German Pat. No. DE-OS 2,845,794 or via a central reinforcement tube which interconnects the two end walls of the low-pressure casing as disclosed in U.S. copending application of J. Belart and F. Wienecke, Ser. No. 061,113, filed July 26, 1979, assigned to the same assignee as the present application. This requires a sealing of the axially movable wall at the point where these tie elements extend therethrough. The sealing necessitates additional structural arrangements and represents a possible source of failure.